This invention relates to a process for selective extraction of copper ions from aqueous solutions with novel benzoin oxime chelate formers into a liquid hydrocarbon.
In recent years, hydrometallurgical processes have achieved increasing importance for recovery of metals, especially for environmental considerations and a relatively low labor requirement. In these processes, the ores are first dissolved in acids or bases. The ore lye obtained is intensively mixed with complex formers dissolved in organic solvents. Depending on the extraction agent and the pH value, only certain metal ions are complexed and transferred to the organic phase. In the specification and claims "extraction agent" means a mixture of the chelate former and a suitable solvent. In this way, the desired metal ions can be separated from impurities. Metal chelates dissolved in the organic phase are subsequently decomposed so that the extraction agent can be recycled for subsequent extractions.
Solvent extraction is widely employed in copper recovery since copper ions form very stable chelates with many extraction agents and the metal value is high. Copper can be separated from other metal ions present in the ore lye, e.g., iron, zinc, cobalt and nickel, as well as other metals, by solvent extraction. Organic phase containing copper chelate is then separated from the ore lye and intensively mixed with dilute mineral acid. With decomposition of the chelate, copper ions are returned to the aqueous phase, whereas the extraction agent is regenerated.
Chelate formers employed for the above process must satisfy various requirements:
(A) The chelate former and copper chelate must be very soluble in organic solvents but practically insoluble in water. High solubility in water would increase costs because of losses of chelate formers and/or copper.
(B) The chelate former, in certain pH ranges, must complex copper ions selectively. The pH of copper ore lyes is generally below 2.
(C) High chemical stability, especially against acids, is required of chelate formers for copper, because most copper ore lyes have pH below 2.
(D) The copper chelate should not decompose under the extraction conditions but must be decomposable into its components by treatment with dilute mineral acids or strippers. This requirement is especially important since the copper is usually deposited electrolytically from the acidic strip solution obtained. If acid concentration of the strip solution is too high, the electrodes dissolve partially and contaminate the electrolytic copper with lead.
(E) It is very important that the emulsions formed by mixing extraction agent with the ore lye separate quickly so as to avoid long settling times.
(F) Rapid chelate formation is critical for economic operation of a continuous countercurrent extraction plant.
Known chelate formers for copper ion extraction only fulfill the above requirements partially. For example, derivatives of 8-hydroxy-quinoline and their copper chelates are only moderately soluble in conventional solvents for solvent extraction. They require relatively strong mineral acids for stripping. Because of their relatively basic properties, they extract acid during stripping so that the extraction agent becomes contaminated with acid.
Aliphatic hydroxyoximes have also been used as chelate formers in extraction agents. Aliphatic hydroxyoximes do not operate quantitatively below pH 1.3. Substituted o-hydroxybenzophenone oximes, which are very effective below pH 1.3, have the disadvantage that chelate formation requires a long time and the copper complex formed can be decomposed only with relatively strong mineral acids.
These disadvantages do not occur with new chelate formers of this invention. For solvent extraction of copper ions according to the present invention, a compound of Formula I, or mixture thereof, can be used.